Scanning optical system

Abstract

A scanning optical system is provided with a scanning lens which images a luminous flux deflected by a deflector at a constant angular speed on a surface to be scanned so that the luminous flux scans the surface to be scanned substantially at a constant speed. At the cross section in the main scanning direction, the luminous flux incident on the scanning lens is a convergent light beam, and the scanning lens includes from the deflector side a first lens of a positive paraxial refractive power and a second lens of a negative paraxial refractive power.

What is claimed is: 
     
       1. A scanning optical system comprising: a deflector which deflects a luminous flux at a constant angular speed, and   a scanning lens which images the luminous flux deflected by the deflector on a surface to be scanned and causes the luminous flux to scan the surface in a main scanning direction substantially at a constant speed,   wherein a convergent light beam is incident on the scanning lens, and wherein said scanning lens includes from a deflector side a first lens element whose paraxial refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative,   wherein the following condition is fulfilled: β>0     where β represents the magnification of the scanning lens in the main scanning direction.   
     
     
       2. A scanning optical system as claimed in claim 1, wherein said first and second lens elements both have their paraxial cross sections in the main scanning direction formed to be of meniscus configurations concave to the deflector side. 
     
     
       3. A scanning optical system as claimed in claim 1, wherein the following condition is fulfilled: 0<β<0.4 where β is a magnification of the scanning lens in the main scanning direction.     
     
     
       4. A scanning optical system as claimed in claim 1, wherein the following condition is fulfilled: f 1  >0 and f 2  <0 where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at the cross section in the main scanning direction.     
     
     
       5. A scanning optical system as claimed in claim 4, wherein the following condition is fulfilled: ##EQU8## 
     
     
       6. A scanning optical system as claimed in claim 1, wherein the following condition is fulfilled: ##EQU9## where L is a distance from a point of deflection to an image plane, and C is a distance from the point of deflection to an image side surface of the second lens element. 
     
     
       7. A scanning optical system as claimed in claim 1, wherein the following condition is fulfilled: ##EQU10## where W is a width of scanning on an image plane, and L is a distance from a point of deflection to an image plane. 
     
     
       8. A scanning optical system comprising: a light source which emits a divergent light beam;   a condenser lens which converts a luminous flux emitted from the light source into a convergent light beam with respect to a main scanning direction;   a deflector which reflects the convergent light beam having exited from the condenser lens at a constant angular speed; and   a scanning lens which images the convergent light beam deflected by the deflector on a surface to be scanned and causes the light beam to scan the surface in the main scanning direction substantially at a constant speed, said scanning lens including from a deflector side a first lens element whose paraxial refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negatives,   wherein the following condition is fulfilled: β>0     where β represents the magnification of the scanning lens in the main scanning direction.   
     
     
       9. A scanning optical system as claimed in claim 8, further comprising a cylindrical lens which images the luminous flux incident on the deflector in a vicinity of a point of deflection of the deflector with respect to a sub scanning direction. 
     
     
       10. A scanning optical system as claimed in claim 9, wherein said scanning lens includes a toric surface such that a paraxial refractive power in the main scanning direction and a paraxial refractive power in the sub scanning direction are different from each other. 
     
     
       11. A scanning optical system as claimed in claim 10, wherein an extended toric surface is formed in the second lens element. 
     
     
       12. A scanning optical system as claimed in claim 11, wherein said first lens element is rotationally symmetrical. 
     
     
       13. A scanning optical system as claimed in claim 11, wherein the following condition is fulfilled: ##EQU11## where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at a cross section in the main scanning direction. 
     
     
       14. A scanning optical system as claimed in claim 8, wherein said first and second lens elements both have their paraxial cross sections in the main scanning direction formed to be of meniscus configurations concave to the deflector side. 
     
     
       15. A scanning optical system as claimed in claim 8, wherein the following condition is fulfilled: 0<β<0.4 where β is a magnification of the scanning lens in the main scanning direction.     
     
     
       16. A scanning optical system as claimed in claim 8, wherein the following condition is fulfilled: f 1  >0 and f 2  <0 where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at the cross section in the main scanning direction.     
     
     
       17. A scanning optical system as claimed in claim 8, wherein the following condition is fulfilled: ##EQU12## where L is a distance from a point of deflection to an image plane, and C a distance from the point of deflection to an image side surface of the second lens element. 
     
     
       18. A scanning optical system as claimed in claim 8, wherein the following condition is fulfilled: ##EQU13## where W is a width of scanning on an image plane, and L is a distance from a point of deflection to an image plane. 
     
     
       19. A scanning optical system as claimed in claim 8, wherein the following condition is fulfilled: S1>L where S1 represents a distance from a deflection point to an object point on which the convergent light would converge but for the scanning line, and L represents a distance from the deflection point to an image point.     
     
     
       20. A scanning lens which images a convergent luminous flux deflected by a deflector on a surface to be scanned and causes the luminous flux to scan the surface in a main scanning direction substantially at a constant speed in a scanning optical system, said scanning lens consisting of from a deflector side: a first lens element whose paraxial refractive power in the main scanning direction is positive; and   a second lens element whose paraxial refractive power in the main scanning direction is negative,   wherein the following condition is fulfilled: β>0     where β represents the magnification of the scanning lens in the main scanning direction.   
     
     
       21. A scanning lens as claimed in claim 20, wherein said first and second lens elements both have their paraxial cross sections in the main scanning direction formed to be of meniscus configurations concave to a same side. 
     
     
       22. A scanning lens as claimed in claim 20, wherein the following condition is fulfilled: 0<β<0.4 where β is a magnification of the scanning lens in the main scanning direction.     
     
     
       23. A scanning lens as claimed in claim 20, wherein the following condition is fulfilled: f 1  >0 and f 2  <0 where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at the cross section in the main scanning direction.     
     
     
       24. A scanning lens as claimed in claim 23, wherein the following condition is fulfilled: ##EQU14## 
     
     
       25. A scanning lens as claimed in claim 20, wherein the following condition is fulfilled: S1>L where S1 represents a distance from a deflection point to an object point on which the convergent light would converge but for the scanning line, and L represents a distance from the deflection point to an image point.     
     
     
       26. A scanning optical system for applying a source of light, comprising: a deflector;   means for converging a light beam from a source of light and applying the convergent light beam to the deflector; and   a scanning lens system for imaging the convergent light beam from the deflector on a surface, including a first lens element whose parallel refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative, wherein the following condition is fulfilled: 0<β0<0.4 where β is a magnification of the scanning lens system in the main scanning direction.       
     
     
       27. A scanning optical system as claimed in claim 26, wherein aid first and second lens elements both have their paraxial cross sections in the main scanning direction formed to be of meniscus configurations concave to the deflector side. 
     
     
       28. A scanning optical system for applying a source of light, comprising: a deflector;   means for converging a light beam from a source of light and applying the convergent light beam to the deflector; and   a scanning lens system for imaging the convergent light beam from the deflector on a surface, including a first lens element whose parallel refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative, wherein the following condition is fulfilled: ##EQU15## where L is a distance from a point of deflection to an image plane, and C is a distance from the point of deflection to an image side surface of the second lens element.   
     
     
       29. A scanning optical system for applying a source of light, comprising: a deflector;   means for converging a light beam from a source of light and applying the convergent light beam to the deflector; and   a plastic scanning lens system for imaging the convergent light beam from the deflector on a surface, including a first lens element whose parallel refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative, and a surface of the second lens element has a toric shape.   
     
     
       30. A scanning optical system as claimed in claim 29 wherein the first lens element has surfaces that are rotationally symmetrical. 
     
     
       31. A scanning optical system as claimed in claim 29 wherein said first and second lens elements both have their paraxial cross sections in the main scanning direction formed to be meniscus configurations concave to the deflector side. 
     
     
       32. A scanning optical system comprising: a deflector which deflects a luminous flux at a constant angular speed, and   a scanning lens which images the luminous flux deflected by the deflector on a surface to be scanned and causes the luminous flux to scan the surface in a main scanning direction substantially at a constant speed,   wherein a convergent light beam is incident on the scanning lens, and wherein said scanning lens includes from a deflector side a first lens element whose paraxial refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative,   wherein the following condition is fulfilled: S1>L     where S1 represents a distance from a deflection point to an object point on which the convergent light would converge but for the scanning line, and L represents a distance from the deflection point to an image point.   
     
     
       33. A scanning optical system as claimed in claim 32, wherein the following condition is fulfilled: f 1  >0 and f 2  <0 where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at the cross section in the main scanning direction.     
     
     
       34. A scanning optical system as claimed in claim 33, wherein the following condition is fulfilled: ##EQU16## where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at the cross section in the main scanning direction. 
     
     
       35. A scanning optical system comprising: a deflector which deflects a luminous flux at a constant angular speed, and   a scanning lens which images the luminous flux deflected by the deflector on a surface to be scanned and causes the luminous flux to scan the surface in a main scanning direction substantially at a constant speed,   wherein a convergent light beam is incident on the scanning lens, and wherein said scanning lens includes from a deflector side a first lens element whose paraxial refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative,   wherein the following condition is fulfilled: ##EQU17## where W is a width of scanning on an image plane, and L is a distance from a point of deflection to an image plane.   
     
     
       36. A scanning optical system comprising: a light source which emits a divergent light beam;   a condenser lens which converts a luminous flux emitted from the light source into a convergent light beam with respect to a main scanning direction;   a deflector which deflects the convergent light beam having exited from the condenser lens at a constant angular speed; and   a scanning lens which images the convergent light beam deflected by the deflector on a surface to be scanned and causes the light beam to scan the surface in the main scanning direction substantially at a constant speed, said scanning lens including from a deflector side a first lens element whose paraxial refractive power in the main scanning direction is positive and a second lens element whose paraxial refractive power in the main scanning direction is negative,   wherein the following condition is fulfilled: ##EQU18## where f 1  is a paraxial focal length of the first lens element at a cross section in the main scanning direction, and f 2  is a paraxial focal length of the second lens element at a cross section in the main scanning direction.